Ultrafast reversal of the ferroelectric polarization by a midinfrared pulse

Abstract

I calculate the ferroelectric polarization dynamics induced by a femtosecond midinfrared pulse as measured in the recent experiment by R. Mankowsky, Phys. Rev. Lett. 118, 197601 (2017)PRLTAO0031-900710.1103/PhysRevLett.118.197601. It is due to the nonlinear coupling of the excited infrared-active phonon mode with the ferroelectric mode or to the excitation of the ferroelectric mode itself depending on the pulse frequency. To begin with, I write the LiNbO3 crystal symmetry invariant thermodynamic potential including electric field and nonlinear phonon coupling terms. I solve the equations of motion determined by this potential for phonon coordinates numerically. I explain the transient polarization reversal observed in the experiment by the action of the depolarizing electric field, which is due to bound charges at the polarization domain boundaries, and give a reasonable estimate for its value. I argue that the polarization can be reversed when this field is screened.